States’ rights is making a comeback, but this time it’s progressives, not slaveholders or white supremacists, raising the cry.

There’s an independence movement in California — the frustrated giant that provided Hillary Clinton’s popular-vote margin of 3 million in November. In a New Republic manifesto, Kevin Baker goes beyond “Calexit” to advocate a quasi-secessionist “Bluexit” for all 20 states that Clinton carried.

Dismayed by the Democrats’ loss of the federal government, gloomy at the prospect of more such defeats to come and — in Baker’s case — embittered by red states’ dependence on federal funds disproportionately supplied by blue-state taxpayers, some lefties have concluded that if you can’t lick ’em, leave ’em.

Or take ’em to court, as blue-state attorneys general are doing to the Trump administration on immigration, in a mirror image of their red-state counterparts’ lawsuits against President Barack Obama on the same issue.

Obviously, a national breakup along state lines is not going to happen, and would make our predicament worse if it did.

Still, stripped of its loopier manifestations, the liberal rediscovery of states as sovereign policymaking entities could be a positive development.

Heretofore, federalism has been a right-wing cause, whose malignant forms trace their pedigree to John C. Calhoun and Secessionism 1.0. Now, a left-right convergence might sustain benign forms of federalism — based on the understanding that policy should, whenever appropriate, be made close to the people who will actually live under it.

Constitutional rights, especially those protected by the Bill of Rights and the Civil War amendments, must be federally enforced without variation. Ditto for the execution of national functions such as immigration, defense and monetary policies.

Beyond that, is it vital that all economic and social policies be identical from Massachusetts to Texas? Or is there some benefit in state-by-state experimentation and even a certain amount of competition?

The United States could not, indeed, survive half-slave and half-free. We certainly could survive if our states’ social models were half-red and half-blue — or one-third red, one-third blue, one-third purple. We might even flourish.

Many would be surprised how close we already are to such a devolution. Policy waivers are available to states that wish to depart from provisions of national education and health legislation — Obamacare included.

The New Deal’s great innovation, the minimum wage, sets a national floor under hourly pay but has long since ceased to function as a national standard. In the nearly 10 years since Congress last adjusted it, multiple states and localities have enacted their own laws. Now 29 states with 63 percent of the U.S. population have minimums higher, often much higher, than the federal $7.25 per hour.

(Video: Jenny Starrs/Photo: Jabin Botsford/The Washington Post)

Twenty-eight states also have right-to-work laws, barring mandatory union dues, but no less a progressive man of labor than Andy Stern, former president of the Service Employees International Union, thinks more decentralization of federal labor law might help unions escape their seemingly terminal decline.

In a recent National Affairs essay, Stern and free-market think-tanker Eli Lehrer called for state waivers under the National Labor Relations Act, so as to enable “experimentation with new business models that could, in turn, vastly increase the number of people involved in labor unions as well as unions’ own success as business enterprises.”

Health care and education are two crucial, and expensive, areas in which the states and the federal government have been involved with each other for so long that it may be impossible ever to disentangle them. Sen. Lamar Alexander (R-Tenn.) advocated a “grand swap” in which the federal government would pay for Medicaid entirely while states would take sole responsibility for schools. Seems a tempting deal for progressives interested in national “single-payer” health care for the poor.

If nothing else, Alexander’s idea would clarify lines of accountability. Clarification might in fact be the greatest benefit of federalism. Part of what aggrieves both the left and the right about the status quo is complex cost-shifting between Washington and the states, which renders government at all levels less transparent. If you doubt it, read Baker’s scornful threat to withdraw blue-state taxpayers’ support for federal disaster-relief aid to the hurricane-prone Gulf states, as payback for voting for Trump.

Ours is an era of troubled continental confederations. The Soviet Union failed because it never should have existed, and never would have, but for the ruthless imperial control that Communists in Moscow exercised over its component peoples.

The European Union decays because it has just enough power to infringe annoyingly on its constituent nations’ sovereignty, but not enough truly to unite them.

America’s federalist constitution, by contrast, offers ways of channeling debates away from Washington — where the stakes are winner-take-all but the processes are deadlocked — into potentially more fluid and productive state channels.

Neither Blue America nor Red America really wants to break up. We just need to give each other some space.